Water and the marine environment in Norwegian harbours are often of poor quality because the sediments are contaminated. New approaches can transform the contaminated sediments to attractive shore properties.
Dredging of contaminated sediments Photos: Trondheim Havn/ Rambøll
In a research project funded by The Research Council of Norway, NGI works with new remediation methods for contaminated coastal and fjords sediments. The project is done as a cooperation between NGI, Norcem, DNV, Rambøll, Skanska and NOAH. The objective is to combine the results of research in the laboratory with the observations from actual projects in Hammerfest and Bærum. The project also uses the experience from a pilot project in the harbour in Trondheim.
The quality of water and marine environment in Norwegian fjords and harbours vary considerably, and the remediation solutions need to be adapted on a case by case basis.
Compact concrete mixture
- Briefly, the method we are developing consists of building a barrier close to the edge of the shore. The contaminated sediments are then dredged and placed inside the barrier and stabilised with binding material, says Magnus Sparrevik from NGI.
The mixing of cement and possibly additives is best done with a gigantic 'wisp', as the mini-versions used for whipped cream. After a day or two, the loose sediment materials have become so stiff that heavy construction vehicles can easily be driven on them.
The contaminated sediments are dredged and placed inside the barrier, then stabilised with binding material.
- The advantage of the approach is that the contaminants are removed while the material is transformed into a useful fill, says Sparrevik. When the contaminated sediments are extracted and stabilised, the chemistry in the masses may change significantly. Leakage may occur on the short term.
It is therefore important to develop mixtures that give enough strength and at the same time enough impermeability to the fill material to ensure minimum leakage of the toxic substances.
Multi-disciplinary research
Such development requires a multi-disciplinary approach, including both geotechnical competence and environmental knowledge. Combining the two disciplines is one of NGI's strengths. - In this project, NGI's laboratories ran extensive tests to determine and optimise the effects of different additives. We wish to also understand in more detail the process of stabilisation and document the method, says Sparrevik.
The work has gained keen interest from abroad, and through the Swedish parallel project StabCon, the NGI project was given Eureka-status under the EU-research umbrella.